The invention relates to a motor control system for a fuel burner, and particularly to a burner motor control system and method for a fuel burner to reduce the efforts of the fluctuation of the power voltage applied thereto.
A conventional motor control system of a fuel burner, as shown in FIG. 1 and FIG. 2, comprises a power source 1 for generating the power voltage required for a fuel burner system, an inputting portion 2 for receiving signals detected which relate to numerous key inputs including the present and the set temperature desirable to the user, as well as states of a frame rod short circuit, an igniter, a blower motor rotation and a burner motor rotation, etc. Also, included is a system control portion 3 for controlling the operation of loads such as the igniter, the blower motor and the burner motor based on the detected signals, and a microprocessor 4 for determining a heating step dependent upon the comparison of the present temperature with the set temperature from the inputting portion 2, and for operating an electronic pump 5 coming up with the heating step and having its program predetermined for feeding a control signal to the burner motor BM so as to assure air necessary for the combustion of fuel injected into a burner 6. The burner motor BM is provided with a photocoupler including a light emitting diode 7 operated by a burner motor driving control signal from the microprocessor 4 and a transistor 7' saturated by the light received from the light emitting diode to initiate a burner motor driving portion 8.
In a conventional system, while power is being supplied to a microprocessor 4, it controls the system control portion 3 in a first stage according to the temperature signal from the inputting portion 2 desirable to user. After the predetermined time passes, the microprocessor 4 determines the heating stage dependent upon the result of the comparison between the temperature set and the present temperature received from the inputting portion 2. The determined stage is applied to the light emitting device 7, to the control data for the operation of the electronic pump 5 and the operating signal of the burner motor BM for supplying air necessary in the fuel combustion to the burner 6. At that time, the transistor 7' called the light receiving element is alternately operated in an on or an off position in response to the signal of the light emitting diode 7 to trigger the gate of a thyristor SCR, so that the burner motor is grounded through a regulating circuit having a bridge circuit BD, constant regulated voltage resistors R.sub.2, R.sub.3 and a constant regulated voltage condenser C.sub.1 which is applied to an AC power source VC. Herein it is known that the thyristor SCR detects the amplitude of the power voltage to control the rotation speed of the burner motor BM. A resistor R.sub.4 and a condenser C.sub.2 not explained are respectively arranged to connect the burner motor BM to the ground.
If the power voltage of the burner motor BM is higher or lower than the reference voltage, a voltage fluctuation changes the amplitude of the power voltage which hinders the stability of the motor speed. It induces the uncompleted combustion of the burner 6 due to the non-uniform volume of air required in a fuel combustion.
A typical technique for maintaining the stability of the amplitude of the power voltage to be applied regardless of the voltage fluctuation is described in U.S. Pat. No. 4,117,384 issued to Armstrong. The Armstrong patent reveals a circuit for processing the a.c. output of a tachogenerator 5 whose frequency is proportional to the speed of a rotor of the tachogenerator, in which a voltage level detection means 7 is responding to the a.c. output, a key pulse producing means G1 is responding to at least one output of the detection means 7 to produce a key pulse whose duration is inversely proportional to the rotational speed, a first gating means G2 or G3 is responding to an output of the detection means and an output of the key pulse producing means to produce a reset pulse after a predetermined period in the interval between each key pulse, and a voltage generator 6 is responding to each reset pulse to provide a predetermined output level and is responding to each key pulse to ramp that output level at a predetermined rate for the duration of that key pulse. Whereby the output level of the voltage generator during each of the predetermined periods is a predetermined function of the rotational speed.
The circuit relates to the detection of the voltage fluctuation in a power source N within the duration of the sample pulses generated by incorporating the first key pulse generating means G1 or G2 into the voltage generator 6 as well as the control of an output voltage regarding the rotation number of the motor. Armstrong does not teach the processing of the fluctuation voltage which is a higher or a lower voltage than the reference voltage of a motor to be fed.
Thus, the amplitude changes of a power voltage to be applied to a load such as a burner motor BM, especially the input voltage fluctuations, need to be compensated. However such a compensation technique is not realized in the prior art.
The main object of the invention is to provide a load control system for rapidly detecting the fluctuations of a power voltage to be applied so as to compensate for it.
Another object of the invention is to provide a load control system for simply realizing the detection of the voltage fluctuation regarding the application of a power source.
Still another object of the invention is to provide a burner motor control system which compensates for the voltage fluctuation of a power source to keep the rotational speed of a burner motor uniform.
Still another object of the invention is to provide a burner motor control method which compensates for the voltage fluctuation of a power source to keep the rotational speed of a burner motor at a constant regulated voltage.